A fluorescent lamp, which is a common type of all lamps, has a mechanism as follows. A fluorescent lamp is provided with an arc tube having a phosphor layer on the inner surface thereof. Mercury and noble gas fill the arc tube. Ultraviolet rays are produced inside the arc tube by mercury excitation when an electric discharge occurs. The ultraviolet rays are converted into visible light by the phosphor layer. As a result, the fluorescent lamp emits light. Conventional glass for such a fluorescent lamp is made of lead glass that contains 4-28 wt % of lead oxide. Today, however, soda-lime glass that does not contain lead oxide is replacing the lead glass for environmental conservation.
When ultraviolet rays penetrate the phosphor layer and the arc tube and leak out of the lamp, discolorment and the mechanical strength deterioration of resin components of luminaire and such as well as lighted objects may occur. Such discolorment and deterioration matter especially when using a fluorescent lamp for display lighting of clothes and art objects. Unfortunately, however, a conventional fluorescent lamp does not sufficiently cut ultraviolet rays (especially ultraviolet rays with a wavelength of 313 nm) generated by mercury excitation. Consequently, the resin components that are susceptible to ultraviolet rays often undergo a problem of discolorment and deterioration.
In view of the above problem, Patent Documents 1 and 2 listed below disclose that glass for lamps containing CeO2 improves the ultraviolet screening capacity. Patent Document 1 also discloses the use of glass containing Sb2O3 used for an arc tube provides a fluorescent lamp that is able to maintain high luminance.    PATENT DOCUMENT 1: Japanese Patent Application Publication No. 2002-137935    PATENT DOCUMENT 2: Japanese Patent No. 2532045